An ionosonde is the most basic method of measuring the electron density in the ionospheric plasma, depending on altitude. An ionosonde measures the distribution of electrons depending on their altitude, and functions by measuring radio waves reflected by electron layers in the ionosphere following vertical incidence of radio waves.

The ionosonde used by the RRA is Digisonde-256, a model produced by the Lowell Center for Atmospheric Research at the University of Massachusetts in the United States. The frequency coverage is 0.1MHz-30MHz and pulse power, bandwidth, and observed frequency are set to 5kW, 20 kHz and 100 kHz, respectively. The result is displayed in the form of an ionogram, a graph showing received data of radio wave reflection. The interpretation of an ionogram provides data on the state of the ionosphere at a specific time when it is being observed.